The invention relates to an X-ray spot-film device. The device comprises a cassette carriage with two sliding fixtures for holding and sensing the cassette. The opening of the first sliding fixture is determined by the height of the cassette while the opening of the second-sliding-fixture is determined by the width of the cassette. The device also comprises a strap which is coupled to the sliding fixture. The strap has a measurable dimensions whose value is determined by the dimensions of the cassette. The X-ray spot film device further includes a device for detecting the value of the measurable dimension.
It is important to know the cassette dimensions when making X-ray exposures in an X-ray spot-film device. This is because these dimensions determine the movement path of the cassette carriage to the exposure position, the angle of aperture of the primary radiation beam for the primary radiation beam diaphragm (which is automatically adjustable in dependence on the cassette format), and the indication for the user.
In an X-ray spot-film device of the kind described above which is known from German Offenlegungsschrift No. 1,858,825, there are provided two straps for determining the cassette dimensions. Each of these straps is coupled to one of the two sliding fixtures and each strap has a measurable dimension whose value is determined by the height and the width of the cassette, respectively.
Therefore, there are also provided two devices for detecting the values of the measurable dimensions. Each detecting device comprises a motor for follow-up control. However, the detecting devices may alternatively comprise measuring potentiometers which are coupled to the straps.
The dimensions of cassettes having nonstandardized formats can be determined by such detecting devices. However this is not really necessary because standardized cassettes (DIN 6832) are usually used.